Thermally stable polymers have many applications in the fields of adhesives, coatings, fibers and ablatives. The requirements for practical, thermally stable polymers include high melting (softening) temperatures, resistance to oxidative degradation at elevated temperatures, resistance to nonoxidative thermolytic processes, and stability to radiation and chemical reagents. These conditions are seldom met by organic polymers, where upper limits to thermal stability are generally in the area of 200.degree. C. Compared with most organic polymers, inorganic polymers are generally stronger, harder, and exhibit the thermal and oxidative stability lacking in organic polymers. Unlike organic polymers, however, these materials usually are rather brittle, insoluble, and sometimes hydrolytically unstable.
For these reasons the study of polymers exhibiting both "organic" and "inorganic" properties has attracted wide attention, particularly the study of cyclic and open-chain phosphazene polymers. However, linear polymers have proved to be very expensive, since they must be prepared from cyclic halophosphazenes of high purity under exacting conditions.